Method of extracting zinc.



w; G. WARING. l,METHOD o1" EXTRAoTlNG zINo.

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UNTTEE s STATES PATENT OFFICE.

WILLIAM GEORGE WARING, OF rIJYRONE, PENNSYLVANIA.

METHOD OF EXTRACTING ZINC.

SPECIFICATION forming part of Letters Patent N o. l718,554, datedJanuary 13, 1903.

Application led June 14, 1902. Serial No. 111,750.

ifo ad whom, it may concern:

Be it known that LWILLIAM GEORGE WAR ING, a citizen of the UnitedStates, residing at Tyrone, Blair county, Pennsylvania, have inventedcertain new and useful Improvements in Methods of Extracting Zinc, ofwhich the following is a specification.

My invention relates toa method of extracting zinc in the form of purezinc suld from crude zinkiferous-ores,metallurgical products orresidues, and from natural or artificial solutions or precipitates,therefrom containing zinc in any state of combination and of separatingthe pure zinc sulfid from all other metallic or earthy combinations.

My method is based upon they following chemical reactions: 1

(A.) The natural and artificial sulfids of zinc, cadmium, and some othermetals are rap# idly and completely decomposed at ordinary temperaturesby acidulated solutions of ferrie sulfate, Fe2(SO'4)2, withtheliberation ofsulfur and the formation of zinc sulfate, dto., asfollows:

ZnS+Fe2(SO4)2=ZnSO4-l-2FeSO4-l-S, (l) the ferrie sulfate being sulfate.

(B.) All oxidized compounds of zinc are soluble in Water acidulated withsulfuric acid-e. g.:

reduced to ferrous The same result is of course obtained when an exactequivalent of hydric sulfid (H2S) is added to the solution-. e., thecopper, silver, and cadmium alone are precipitated.

(No specimens.)

(D.) If hydrogen suliid (H28) be conducted into a dilute solution ofzinc sulfate, such as results from the last-named operation undercertain conditions hereinafter to be specified, the whole of the zincmay be precipitated as pure White zinc suld, with the liberation of anequivalent of sulfuric acid, thus:

Under the conditions to be prescribed no other metals or compounds ofany kind are precipitated along with the zinc sulfid, so that the latterwhen separated from the iiuid by decantation or filtration is at onceavailable as a pure white pigment or after calcination as oxid for useas a pigment or for the preparation of chemically-pure metallic zinc.

(E.) If the acid solution resulting from the last-named reaction andcontaining ferrous sulfate be aerated by exposure to the atmosphere at asuitable temperature, the ferrie sulfate is regenerated at the expenseof a molecule of sulfuric acid for every two molecules of ferroussulfate, thus:

Although it is stated in nearly all, if not all, r

chemical treatises and text-books that zinc is not precipitated fromacid solutions by H2S, Berzelius long ago noted that it is partiallyprecipitated by H2S from saturated neutral solutions. Eliot and Storernoted later that ZnS may be precipitated by H28 from the sulfate orchlorid in the presence of very dilute sulfuric or hydrochloric acid,and invl888-89 Baubigny reported that a neutral solution of the sulfateor chlorid containing 0.3 per cent. of either salt may be completelyprecipitated after saturation with the gas and after standing severalhours. This chemist also noted that if the solution be heated thirty toninety times the amount of acid combined with the zinc must be presentin a free state to prevent any precipitation. He regarded thedecomposition of ZnSO4 by H2S as a function not only of the weight ofthe free acid to the weight of the metal, but also of the acid to themetal. (Comi/ot. Rend., OVH, 1148.)

H28 has long been in use in analytical work to separate zinc as suldfrom acetic solutions, zinc suld being quite insoluble in acetic acid;but in all cases heretofore recorded, so far as I have been able tolearn, the solutions have been subjected to the action of a large excessof the gas, a procedure which is unsuited to economical operations upona large scale.

To carry out successfully upon the large scale a method of separatingzinc from impure sulfate solutions by means of hydrogen sulfid it isessential, first, that the solvent solution shall be capable of easyregeneration without consumption of acids or other expensive chemicals;second, that the precipitant (H28) shall be capable of separating nearlyor wholly its equivalent of metal.

In my researches, undertaken to elucidate the problem, I discovered thatvery dilute acid solutions of ferrie sulfate containing not more than0.6 to 1.2 per cent. of free acid and much less ferrie salt are muchmore energetic in their action at ordinary temperatures upon zinkiferoussulfids than are strong solutions. Thus a natural mine-water containing0.34 per cent. metallic zinc and 0.29 per cent. iron as sulfates,together with a little copper and cadmium, after complete precipitationof the zinc, copper, and cadmium as sulids by H28 dissolved immediatelyafterward 0.33 per cent. of zinc from ordinary zinc-blende concentratesupon passing over the surface of the concentrates for a distance of onehundred and sixty feet in ten minutes time without further exposure tothe atmosphere than was gained during the lixiviation, which wasconducted inaslightly-inelined trough. After a second precipitation withH28 precisely the same amount of zinc was again dissolved in the sametime and under the same conditions and no diminution was found even upona third repetition of the process.

In regard to the second requirement I find that at the ordinarytemperatures (o to 80o Fahrenheit) under the most favorable conditionsonly about four-fifths of the amount of zinc equivalent to the amount ofH28 conducted into the solution is precitated as suliid from neutral orslightly acid solutions containing 0.8 per cent. or less of metalliczinc in the form of sulfate. Somewhat less is separated from chloridsolutions. If the temperature of the solution is raised to about 100Fahrenheit before the addition of the gas, the passage into the solutionof a large excess of gas does not increase the amount of zincprecipitated. If the temperature be below Fahrenheit, 99.5 per cent. ofthe zinc is separated as sulfid from a solution containing 0.8 per cent.of the metal by using an excess of the gas. The same result is reachedin the case of solutions containing 0.3 to 0.5 per cent. of metalliczinc, when only the exact equivalent of the zinc present is added in theform of H28, and the temperature of the solution is afterward altered byheating to 160 to 180 Fahrenheitthat is, ninety-five to ninety-nine percent. of the zinc separates as suld; but the suld separated under suchconditions is apparently a dierent substance from that separated at theordinary temperature. It is a pure white amorphous heavy powder,subsiding quickly and easily sepa# rated by filtration. Chemically,T itis Zn8,while the more slimy and slowly-subsiding compound precipitatedat the ordinary temperature appears to be zinc sulfid containingoceluded hydrogen sulfld to an amount equivalent, approximately, totwenty-five per cent. of the precipitate. Further investigation isnecessary to establish the nature of the physieochemical reactions whichoccur when H28 is conducted into a dilute aqueous solution of zincsulfate at the ordinary temperature and when the mixture is subsequentlyheated; but I have fully proved by numerous trials that under theconditions just named the precipitation corresponds nearly enough totheory to make it practicably available, and at the same time it yieldsa solution nearly absolutely void of free H28 and at the righttemperature for rapid oxidation and rapid solution of natural sulids.Under the conditions mentioned, as already stated, no trace whatever ofiron, manganese, nickel, or other metals is thrown down with the ZnS.

The presence of the already-precipitated zinc sulfid in the solution isabsolutely essential before the temperature is raised. If theprecipitate be separated and the solution alone heated, no furtherprecipitation occurs.

My process founded upon the foregoing reactions and my researchesthereupon are as follows: The ores or zinkiferous materials to betreated may consist of raw natural sulds and of calcined orotherwise-oxidized zinkiferous material, or they may consist wholly ofoxidized substances. They are to be lixiviated either in beds, troughs,vats, or in their natural position in Veins or deposits by means of alixiviating solution, which for oxidized material consists of ordinaryor mine water containing not more than 1.5 per cent. of free sulfuricacid. For sulfid ores the solution must contain in addition to the freeacid a Very small amount of ferrous or ferrie sulfate in solution, whichexerts a catalytic action in the presence of the air at all ordinarytemperatures, effecting the decomposition of the sulfids and theformation of sulfates, as it is alternately oxidized by the air with theabsorption of a molecule of sulfuric acid and reduced byy its actionupon the sultid, to the metallic component of which it yields the acidso absorbed. (See reactions 1 and 2.)

It is to be noted that there is no actual loss of sulfuric acid due tothe reaction 4. A molecule of free acid is merely combined with twomolecules of ferrous sulfate, to be afterward liberated in the freestate upon precipitation of the zinc by H28. Actual loss or tying up offree acid can only occur when the material to be lixiviated containscarbonate or oxid of calcium or magnesium or carbonate IOO IIO

lpossibly other metals of manganese or iron soluble in the lixiviatingmenstruum,butnot decomposable by H28. In such case the loss may berepaired by subjecting the aerated liquor containing much iron -to theaction of-the master-gases containing 802, when the following reactionoccurs:

resulting in an increment of one additional molecule of free sulfuricacid for two atoms of iron presentas ferric sulfate, or the acidity maybe restored by passing it over or through calcined or oxidizedzinkiferous material which has itself been previously moistened andexposed to roaster-gases containing SO2, followed by exposure to theair, whereby sulite of zinc is rapidly converted to zinc sulfate, whichbeing taken into solution yields free sulfuric acid upon precipitationwith H28. After passing through the ore and becoming saturated to thelimit of the free acid originally present with zinc, cadmium, and othermetals contained in the ore the lixiviant is first conducted into a tankor set of tanks'in which the metals whose sulds are absolutelyunaffected by dilute mineral acids (Ou, Cd, Hg, Ag, Bi) are to beseparatedl either by the addition of a small and definite amount of H28gas or by the addition of an exact equivalent or slight excess ofprecipitated zinc sulfid accompanied by agitation. I prefer the use ofZnS in slight excess for this purpose. The excess does no harm and istaken up in subsequent purifications. l/Vithout heating, the clearsettled solution containing Zn, Fe, and

Whose sulfids are soluble in dilute or moderately dilute mineral acids(Mn, Ni, Co, U, 85o.) is then drawn olf into another vat or tank orseries of tanks provided with tight-fitting covers, where itis subjectedto the action of a measured quantity of H28 gas corresponding to theamount of zinc contained in the liquor, the gas be ing admitted undersuitable pressure through asuitable conducting-tube. When the properamount of gas has been admitted, the mixture is to be heated by theadmission of steam through non-corrosive conducting-pipes until theprecipitation of the ZnS is completed, which occurs usually between 160oand 180 Fahrenheit. The subsidence of the precipitate being very rapid,the lixiviant solution can be drawn of immediately after agitation hasceased, and it is at once ready to use again as a lixiviant bypassingitthrough raw or calcined ores, &c.,orin case ordinary minewaters(many of which yield 0.3 per cent. or more of metallic zinc as they arepumped from the mine) are used as the source of zinkiferous liquors theyare returned to the subterranean channels connected with the oredeposits through an opening located some distance from thepumping-shaft.

Vhen the repeated use of acidulated water upon very impure ores orotherzinkiferous material has caused it to be completely saturated withsulfates of iron, manganese, alumina, magnesia, &c.`, the sulfur contentmay be utilized in the greater part, if desired, by precipitation ascalcium sulfate, along with the metallic hydroxids, using quicklime as aprecipitant, calcining the precipitate with coal, and liberating thesulfur as H28 by treatment of the resultant CaS with limekilngas orcarbon dioxid from any source. To replenish the lixiviant, however, itis not necessary to use fresh acid. A fresh supply of convenientstrength can always be produced by the lixiviation of calcined oroxidized zinkiferous material with ordinary water charged with 8O2 fromroaster-gases, which easily yields a solution containing 0.5 to 1.5 percent. metallic zinc as sulfite and sulfate, which solution upon exposureto the air is rapidly converted wholly to sulfate and yields therequired free acid upon precipitation with H28, as previously stated.

After the ore has been completely deprived of zinc, if it is composed ofnatural sulfids, the residue will consist of earthy matters mixed withall the sulfur in a free state that was previously combined with thezinc, copper, cadmium, dto., already dissolved out. It will contain alsoall the lead, silver, and gold, and practically all the pyrite and oxidsof iron and manganese originally present. Being rich in free sulfurand-freed from zinc blende, it can be calcined at a very lowtemperature, yielding a large amount of sulfurdioxid fumes, a portion ofwhich-namely, the amount derived from the liberated sulfur andcorresponding theoretically to the quantity of H28 employed inprecipitation, together with so much 8O2 derived from the combustion ofpyrite (always associated with zinc suld in ores) as may be required tomake up the losses-may be used for conversion into H28, either byreduction with glowing carbonaceous material in presence of steam or byabsorption in lime and reduction with coal, followed by treatment of thecalcium-sulfid product with limekiln gas or CO2 from any source for theliberation of H28. The calcined residuum from silver and gold bearingzinkiferous suliid ores is now in the best possible condition for theeconomical extraction of its lead, silver, and gold by smelting in alead-smelting furnace and is to be so treated. If necessary, it may beagain leached after calcination with the acidulated water for thepurpose of extracting any zinc or copper that may have escapedextraction in the first lixiviation before being sent to the smeltery.

The precipitate obtained from the iirsttreatment of the leach liquorafter lixiviation and containing all the silver, copper, cadmium, &c.,extracted from the ore, together with such excess of zinc sultid as mayhave been added, is to be removed from the coppercadmiumprecipitation-tank and subjected to the following special treatment,viz: First,

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if it contains a large excess of Zinc sulid the greater part of this maybe removed by stirring it with ordinary lixiviating liquor which hasbeen charged with copper sulfate by leaching cupriferous material, beingcareful not to add quite as much copper as is chemically equivalent tothe zinc contents of the precipitate,for after all the zinc sultid hasbeen decomposed by copper sulfate cadmiu m suliid is acted upon in thesame manner. The clear liquor now containing zinc in solution isreturned to the regular course of treatment for zinc and thesilver-copper-cadmium residue (containing also bismuth, palladium, 85e.,it' these'were present in the ore) is heated to the boiling-point in aporcelain-lined vessel with dilute sulfuric acid containing fifteenpercent. HZSOJ, whereby the cadmium is alone dissolved, along with anyzinc suld remaining, leaving the silver and copper sulids, dsc., as auinsoluble sediment. The clear solution is decanted or drawn oft, theresidue diluted with cold water, and filter-pressed, the filtrate beingadded to the stronger decanted iluid, and the mixture of iuids is aftercooling subjected to the action of a stream of H2S,'by which means thewhole of the cadmium is thrown down in the form of pure brilliant yellowor orange colored suld, salable after washing, filter-pressing, anddrying, as cad- The acid solution resulting is to be added to thegeneral stock ofleach liquor.

The copper-silver sulfid residue is to be calcined and smelted intometal, which is to be treated by ordinary electrolytic methods for theseparation of the metals.

It is to be noted that the copper-sulfate solution used to extract thezinc from the cadminin-copper-sulfid precipitate must be free fromferrie salt, which, if present, should be rst reduced by treating theliquor with roaster-gases.

It has been already stated that the H28 required for the precipitationof the zinc, copper, cadmium, silver, &c., may be obtained indirectlyfrom the sulfur contained in the original ores treated when these aresulid ores, so that in such case the process is regenerative throughoutas regards the zinc extraction, the only elements actually consumedbeing fuel, ore, and air. In the case of minewaters being used as thesource of zinc, duc., the residues of lixiviation being left underground, the larger part of the sulfur required may be obtained bycalcination of the zincsultid precipitate, waste being made up bycalcining pyrite, blende,&c. In case ot blende or other ores of zincassociated with heavy spar, the residuum of the leaching operation beingbarium sulfate, this latter may be utilized as a very convenient meansof supplying HZS, yielding pure barium carbonate as a by-product. Thesullid of barium resulting from the calcination of barium sulfate withbituminous coal is very soluble in hot water and from the hot solutionlimekiln-gas liberates HZS gas and precipitates BaCO3.

In the case of purely-oxidized ores being subjected to lixiviation andtreatment of the solution with HQS according to my method either calciumsulfid or barium sultid derived from the reduction of gypsum or heavyspar by coal may be used as the source of HZS, and, if desirable, thesultates may be regenerated by means of sulfur dioxid derived fromcalcining the precipitated metallic suliids.

It is not necessary that the H2S gas used in the process shall be eitherpure or concentrated. Good results have been obtained by me in theprecipitation of Zinc suld from mine-Waters in tanks holding one hundredcubic feet of Water by using gas containing under one per cent. ofactual H28 as a precipitant. Gases containing twenty to thirty per cent.ot' H2S may be easily obtained from the action of liinekiln-gases uponcalcium sulfid or barium suliid, and quite pure H23 is obtainable frombarium suld by its decomposition with pure carbon dioxid derived fromthe action of a stock solution of sodium sulte saturated by ordinaryroaster-fumes containing SO2 upon the precipitated barium carbonateobtained in a prior operation. In this ease the sodium sultite isregenerated, insoluble barium sulte precipitated, (which is againreduced to sullid by ignition with coal,) and pure CO2 liberated, whichin turn liberates pure H28 from a heated solution of barium sulfid.

In case it is desired to carry on the manufacture of zinc chlorid inconnection with the process described pure HZS may be obtained from thedecomposition of zinc sulid with hydrochloric acid. In this ease thedecomposition is carried on in stills, about forty per cent. of the acidused being volatilized and again condensed, while the H25 is liberatedas a pure gas, as described in my application for patent of this datefor a process of manufacture of zine chlorid.

To carry out my process, as described, there are required leaching-vats,launders or beds, storage tanks or reservoirs for the liquors,precipitating-tanks provided with the necessary fixtures of inlet andoutlet pipes, forcepumps, launders, a Waste-gas tower for utilizingnearly-spent gases, a gas-holder with force-pump and all necessary pipeconnections and meters, refining vessels for the treatment ofcadmiferousprecipitates, calciuing-furnaces with dust-settling flues andexhaust-fan, and the necessary appliances for the regeneration othydrogen sullid, which may preferably consist of calcining-furnaces forreduction of alkali-earth sulfates to sulids, grinding apparatus,leach-vats, (in case of BaS,) and closed steam-heated gas-generatingtanks connected with the gas-holder on one hand and the source ot'carbon dioxid isupply upon the other. This may consist ICO simply of anordinary dame-fired limekiln provided with gas conducting and coolingtubes and a gas-forcing pump.

In the drawings I have shown in diagrammatic form the principalapparatus required in carrying out my invention.

I have stated that HZS may be produced by the reduction of the SO2contained in the roaster fumes accompanied by steam by means ofcarbonaceous fuel by the ordinary Water-gas process. I have alsoobtained H28 by the direct action of superheated steam upon zinc sulfidand upon blende; but further experiment is necessary to prove Whethereitherl of these methods can be used economically.

It Will be understood that my invention includes the equivalent of theagents referred to herein and that When free sulfuric acid is mentionedits equivalent is free hydrochloric acid in a less percentage, asstated. The leaching or lixiviating agent used, according to therequirements, is the dilute acidulated Water containing not more than1.5 per cent. of free sulfuric acid or free sulfuric acid with ferriesulfate, or I may use Water containing not more than 1.1 per cent. offree hydrochloric acid or ferric chlorid and free hydrochloric acid asthe leaching agent. I also Wish itgunderstood that the hydrogen suld andthe zinc sultid are equivalents in the preliminary precipitation, or Imay use zinc sulid and hydrogen suliid together for this purpose.

That I claim is- 1. The hereinbefore-described process,con sisting inleaching zinkiferous ores residues, metallurgical products, or naturaldeposits, With a weakly-acidulated Water, containing not to exceed 1.5per cent. of free sulfuric acid, or its equivalent of other mineralacid, precipitating the metals of the copper group by agitation with asoluble sulfid, and iinally separating the zinc by means of hydrogensulfid, substantially as described.

2. The process herein described, consisting in leaching crudezinkiferous ores, residues, or products, by a leaching agent cnsistingof dilute acidulated Wat-er containing not more than 1.5 per cent. freesulfuric acid together With an indefinite amount of dissolved ferriesulfate; precipitating the metals of the cop. per group by agitationWith a slight excess of a soluble sullid, and finally separating thezinc by means of hydrogen sulid, substantially as described.

3. The process herein described, consisting in treating zinkiferousmine-Waters containing metals of the copper-silver-cadmium group insolution by the use of precipitated zinc suliid or its equivalent, inamount chemically equivalent to or slightlyin excess of the Inetals ofthe copper group present in the Waters and finally separating the zincby means of hydrogen sulfid, substantially as described.

4. The method of separating Zinc as pure Zinc sulfid, fromdilute-solutions consisting of either natural mine-waters, or theproducts of artificial lixiviation of zinkiferous materials, containingnot more than one per cent. of zinc and other metals Whose sulids areinsoluble in extremely-dilute mineral acids, in solution, either assulfates or chlorids, and containing also the soluble salts of any orall other metals, which method consists in precipitating the metals ofthe copper-silver-cadmium group as sulids, by adding thereto theirequivalent or a very slight excess, of a soluble suld, drawing olf theclear solution after the subsidence of the sultid named, and subjectingit to the action of an additional amount of hydrogen sultd, equal to, orin slight excess over, the equivalent of the zinc present in solution,for the purposeof partially separating the zinc as sulfid, and finallysubjecting the solution to a temperature of '150 to 180 Fahrenheit forthe purpose of completing the separation of the zinc suld in a purestate and regenerating the acid of the solution, so that it may be usedfor leaching with the same elfect as before, substantially ashereinbefore described.

5. The method of extracting zinc, cadmium and other metals from ores,metallurgical products, residues, or precipitates, containing zinc,orzinc and any other metal,or metals, which consists in leaching suchores, products, residues, or precipitates, with a very diluteacidulated, aqueous solution containing not more than 1.5 per cent. offree sulfuric acid or its equivalentgrsubjecting the leach liquor, orfiltrate, to treatment With precipitated Zinc sulid as described inamount equal to, or slightly in excess of, the equivalent of the metalsof the coppercadmium -silver group present in the solution, for thepurpose of separating them as sultids; decanting or drawing off theclear liquor from such precipitated suliids and subjecting it to actionof a quantity of hydrogen-sullid gas in amount equal to, or slightly inexcess of, the equivalent of the zinc contained in the solution;subsequently heating the solution to effect complete separation of thezinc suliid; decanting or drawing off the clear liquid to be used overagain, Washing, filter-pressing and drying the 'precipitated sulfid, asbefore described.

6. The process of extracting zinc, copper, cadmium and other metals fromsubterranean deposits Without raising their respective ores to thesurface, which consists in supplying to the higher parts of suchdeposits, through a suitable opening, Water containing free sulfuricacid to an amount not exceeding 1.5 per cent. or its equivalent togetherWith any amount of a salt of iron in solution; pumping the mine-waterfrom the lower parts of such deposits or veins; subjecting the waterthus obtained to the action of a denite amount of precipitated zincsuld, or of hydrogen sulfid corresponding to, or slightlyin excess of,the

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equivalent of the metals of the copper-silverdrying the precipitatedzine sulid so ob- Io oadmiumgroup presentin the solution; drawtained,substantially as described.

ingo the clear solution and precipitating the In testimony Whereor` I axmy signature zine therefrom as zinc suld by means of an in presence oftwo witnesses.

equivalent amount of hydrogen sulfid introduced into the solution;heating the solution; WILLIAM GEORGE WARING' drawing o the clear acidfluid and returning l Witnesses:

the same to the subterranean mineral deposl A. M. HULL,

its and finally washing, filter-pressing and GUY H. WARING.

